Fix for error when cancel uploading before success

[Jerome-1010]

Since this.placeholderDelta is updated only when the image upload is successful, the following two problems were occurring.

1. If the process was aborted before a successful upload, calculartePlaceholderInsertLength would refer to null properties and generate an error. 6ebbba7
2. this.placeholderDelta was never reset, so this.placeholderDelta obtained during the last upload could be referenced at the next upload timing. 365cc47

These errors occur when the following functions are passed to the upload property.

options: {
  upload: async (file) => {
    if (file.size > 10 * 1024 * 1024) {
      throw new Error('A file size exceeded!');
    }
    return uploadFunc(file);
  },
},

[maykon-oliveira]

Close #38

[victorLessa]

The problem that this PR intends to solve avoids the need to force the solution presented above, not every case is resolved with the previously suggested behavior